This invention relates to a brake system control.
Automotive vehicles have been produced or demonstrated with brake systems that modulate brake force during stops to provide anti-lock brake control (ABS) and/or that modulate brake force during vehicle acceleration to provide positive acceleration traction control (TCS). Some such brake systems additionally provide brake-by-wire control.
More recently, vehicles have been produced with brake systems that activate in certain situations where some or all vehicle tires are experiencing excessive lateral movement relative to the road surface. The brakes are selectively controlled to attempt to bring the vehicle to a desired course and/or to minimize the lateral movement of the tires relative to the road surface.
It is an object of this invention to provide a brake system control method according to claim 1.
Advantageously this invention provides a brake system control method for actively controlling the road response of a motor vehicle.
Advantageously this invention provides a brake system control method and apparatus that provides a control of vehicle slip angle, for example, by selectively activating vehicle wheel brakes to reduce a difference between actual vehicle slip angle and a desired vehicle slip angle.
Though vehicle slip angle is difficult to measure directly, an advantage provided by this invention includes a dynamic observer for estimating vehicle slip angle. Advantageously the dynamic observer is iterative, providing estimations of vehicle slip angle, vehicle lateral velocity, tire slip angles and lateral forces of the front and rear axles. Each most recent estimation of lateral velocity is used as an input along with vehicle speed and measured vehicle yaw rate to estimate side slip angles of the front and rear tires. The tire side slip angles are the differences between the rolling direction (non lateral) and actual direction of the vehicle tires. The estimated tire side slip angles are used with the estimated lateral coefficient of adhesion between the vehicle tires and the road surface to estimate lateral tire forces. A model within the observer uses the estimated lateral tire forces, lateral acceleration of the vehicle, yaw rate of the vehicle and vehicle speed to estimate the next iteration of vehicle lateral velocity and vehicle side slip angle.
Advantageously, the observer balances the reliability of the model with feedback from sensor measurements, provides estimates in both linear and nonlinear ranges of handling behavior on various coefficient of adhesion surfaces and includes compensation for the errors caused by bank angle of the road.
Advantageously, according to one example, this invention provides a brake system control method, comprising the steps of: measuring a set of vehicle parameters including steering wheel angle, vehicle speed, lateral acceleration and vehicle yaw rate; responsive to the measured parameters using an observer to estimate lateral velocity of the vehicle, wherein the observer contains (a) an open loop dynamic model of the vehicle responsive to the measured vehicle speed and the measured yaw rate, (b) a closed loop term responsive to a first error between the measured yaw rate and a predicted yaw rate, a second error between a previously estimated derivative of lateral velocity and a predicted derivative of lateral velocity and a third error between the measured lateral acceleration and a predicted lateral acceleration; estimating a vehicle slip angle responsive to the estimate of lateral velocity; determining a control command responsive to the vehicle slip angle; and controlling an actuator responsive to the control command.
Advantageously, according to another example, this invention provides a brake system control method comprising the steps of: estimating a front side slip angle of front vehicle wheels; estimating a rear side slip angle of rear vehicle wheels; estimating a first lateral force of the front wheels on a road surface responsive to the first side slip angle; estimating a second lateral force of the rear wheels on the road surface responsive to the second side slip angle; wherein the first lateral force estimation is responsive to a first function for low values of the front side slip angle and responsive to a second function for high values of the front side slip angle; wherein the second lateral force estimation is responsive to a third function for low values of the rear side slip angle and responsive to a fourth function for high values of the rear side slip angle; estimating a vehicle lateral velocity responsive to the first and second lateral force estimation; estimating a vehicle slip angle responsive to the vehicle lateral velocity and a vehicle forward velocity; determining a control command responsive to the estimated vehicle slip angle; and controlling a chassis system actuator responsive to the control command.
According to a preferred example, the first lateral force estimation is responsive to the first function when a first product of the first side slip angle and an estimate of surface coefficient of adhesion is below a first threshold and responsive to the second function when the first product is not below the first threshold, and the second lateral force estimation is responsive to the second function when a second product of the second side slip angle and the estimate of surface coefficient of adhesion is below a second threshold and responsive to the fourth function when the second product is not below the second threshold.